This invention relates generally to color digital cameras, and more particularly to the processing of color data generated by the sensor of a color digital camera.
Digital color cameras are used with computer or other digital processing systems. Such cameras include a sensor array, optics, preprocessing electronics, and a cable or other communication link to transfer data to the digital processing system. Digital cameras are made by Connectix, Intel, and others.
Digital cameras of the prior art often include a solid state sensor including a mosaic of red (R), green (G) and blue (B) sensor elements. Data from the sensor is transmitted to a data processing apparatus to be processed into a series of digital images. However, since there are typically many thousands of sensor elements on a sensor, and since digital video requires frequent updates (“refreshing”) in the order of 20-30 times per second, it is not typically practical to provide a transmission medium that is fast enough to send all of the data available from the sensor to the data processing apparatus. In the past, this problem has been addressed by lossy compression techniques that discards a considerable portion of the video data available from the sensor.
Some of the prior art compression technologies provide an interpolation step which occurs before compression. The interpolation step provides collocated RGB values, and allows for luminance/chrominance re-mapping as well as color correction on the chip. While these other design approaches allow the use of standard and well-known technologies, they are very inefficient because they generate 24 bit data in the chip, which is then compressed and sent to the host.
The sensors used in digital cameras are often of the “mosaic” sensor type, where red (R), green (G), and blue (B) pixels are arranged in a matrix. With mosaic type video sensors, groups of pixels are assembled into blocks for processing through conventional compression techniques. This compression is desirable due to the typically limited bandwidth of the connection mechanism between the camera and the digital processing system. A common form of compression utilizes a discrete cosine transform (DCT).
An advantage of using a mosaic type sensor is that it has only one color value per pixel, which allows for rapid compression of the color sensor data. Of the mosaic type video sensors, the “Bayer-2G” mosaic sensor interesting in that it gives twice as many green pixels as red or blue pixels. Green pixels are good for detecting luminance (brightness) values. However, the Bayer-2G mosaic also makes it more difficult to preprocess the color data. That is, the Bayer-2G sensor places the green pixels in a crosshatched pattern, as seen in prior art FIG. 1, which makes the assembly of blocks for compression relatively difficult.